Ukrainian sailors were on Tuesday filmed giving what Kiev said were forced confessions and brought to court after Russia seized their ships off the coast of Crimea in a major escalation of tensions. A court in Crimea ruled on Tuesday that 12 of the 24 captured sailors and security service agents would be kept in confinement for two months, with a decision on the rest expected Wednesday. Moscow has defied Western calls to release the men, who have been accused of violating Russia's borders and face up to six years in prison. At least three of the men are in hospital. State television has broadcast footage from the interrogation of three of the captives, including an officer who, while reading from a screen, said the ships had deliberately ignored Russian requests to stop. The head of the Ukrainian navy said the sailors had been forced to give false testimony, noting that several of the men had relatives in Crimea. Russian ships rammed a tugboat and opened fire on two gunboats that were trying to reach the Ukrainian port of Mariupol through the Kerch Strait on Sunday. A Russian FSB security service officer escorts a detained Ukrainian sailor to a courthouse in Simferopol, Crimea Credit: STR/AFP/Getty Images The Ukrainian security service said Tuesday that a Russian jet had also fired rockets during the incident, seriously injuring one officer. Special forces later boarded the vessels. Russia has claimed the incident was a planned “provocation,” while Ukraine has called it an act of aggression. Although the Azov Sea is by a 2003 treaty supposed to be shared between Ukraine and Russia, the Kerch Strait connecting it to the Black Sea has been controlled by Moscow since it annexed Crimea in 2014. Russia has been demanding that ships receive permission to pass after it opened a bridge over the strait in May. In a phone call with German chancellor Angela Merkel late on Monday, Vladimir Putin, the Russian president, accused Kiev of “creating yet another conflict situation” before March's presidential election in Ukraine, according to a Kremlin read-out. On Tuesday, Russian state media footage showed Bal anti-ship missiles moving from Sevastopol to the Kerch Strait. For over four years, Russia has backed separatists in a conflict in Eastern Ukraine that has killed more than 10,300 people. Tensions have also been rising in the Azov Sea as both sides have detained each other's fishing vessels. But Sunday's incident marked the first time Russia has openly attacked Ukrainian forces. Crimean bridge map The UK has condemned Russia's “destabilising behaviour in the region and its ongoing violation of Ukrainian territorial integrity”. At an emergency session of the United Nations on Monday, Russia said the Ukrainian vessels deliberately did not wait for permission to pass through the strait, which was temporarily closed. The passage under the bridge had been blocked with a tanker. But Ukraine said its ships had waited for permission and began withdrawing from the area after they were buzzed by Russian helicopters. Speaking on CNN on Tuesday, president Petro Poroshenko said Russia had concentrated a large number of troops near Ukraine's borders, citing Nato intelligence. Ukraine's parliament had previously agreed to impose martial law after Mr Poroshenko claimed he had information that Russia was planning a ground operation. Dispatch: Years of war in Ukraine leaves one million on the breadline It had looked as though March's presidential election, in which Mr Poroshenko is trailing in the polls, would be delayed. But following a backlash, the measures were watered down and will be implemented for only one month and only in 10 regions. The incident will likely boost the ratings of both Mr Putin and Mr Poroshenko. Since the annexation of Crimea, Russia has imprisoned several Ukrainians in controversial trials, including Crimean director Oleg Sentsov. In 2016, military pilot Nadiya Savchenko was sentenced to 22 years in prison by a Moscow court after being captured in eastern Ukraine. Within weeks, she was swapped for two Russian soldiers captured in eastern Ukraine.